Résumé

Phagocytosis is initiated through binding of a particle by receptors that trigger actin polymerization at the site of
contact. Previous studies showed a focalized exocytosis of membrane from internal vesicles at the phagocytic cup.
Components of SNAREs are essential for this process. Synaptotagmins (Syt) are a large family of membrane proteins
that contains two Ca2+-C2 domains which can bind phospholipids as well as SNARE components. Although they
were identified and widely studied in neuronal cells for their role in the regulation of neurotransmitters exocytosis, few studies have demonstrated the expression of synaptotagmin isoforms in macrophages. Several signaling
molecules, including members of the protein kinase C (PKC) superfamily participate in the regulation of actin
polymerisation and phagolysosome biogenesis. Using a proteomic approach, we identified Syt V as a new potential
partner to PKC-a in regulating phagocytosis. We showed that Syt V is expressed in macrophages and that a large
part is localized on recycling endosomes. Moreover, we observed the recruitment of Syt V to phagosomes containing
various particles of wich Leishmania donovani indicating that Syt V is recruited independently of the phagocytic
receptors involved. We also demonstrated an early recruitment of Syt V in macrophages and an accumulation
throughout the maturation process notably for both promastigote and amastigote forms of Leishmania donovani.
Silencing of Syt V by RNAi revealed a key role for this protein in the regulation of phagocytosis. Collectively, these results showed for the first time the importance of Syt V in the regulation of an important innate function of
macrophages and suggest that Syt V acts as a positive modulator of exocytosis with a key role in the regulation of
focal exocytosis during phagocytosis.